I've been using Plex for probably 5 years now and it's the best (only?) software I know of for its purpose, but I haven't seen it "getting better and better" as you say. From my perspective it's had more or less the same useful functionality since I started using it, and my biggest annoyances with it -- the overall flakiness of the apps, syncing, and Chromecast integration, as compared with Netflix -- haven't gotten any better.

But I'm still really glad it exists and don't really feel I have much right to complain about a free (for me) product.

(Edit: okay, to give credit where it's due, I just remembered they did actually fix my biggest annoyance with the iOS app -- previously when you deleted a downloaded video it didn't actually delete it from disk -- there was no way to recover the storage, other than deleting the app itself. So I'd have to reinstall the app every time I took a flight more or less. But they fixed that, you can actually delete things now.)